Optical adapters are known in the industry which can be coupled to an image acquisition device, in particular for microscopic observation.
This adapter typology allows transforming an image acquisition device, e.g. a generic cellular telephone (typically a so-called smartphone) or a tablet, into a high-resolution microscope. In particular, electronic devices such as smartphones and tablets have an integrated photographic optical system, which is often capable of changing its focal distance (mems|cam™ Technologies autofocus system or voice coil motor). Of course, the optics of such devices is designed for macroscopic photographic applications. In order to switch to high-resolution microscopic observation, it is necessary to use a lens with high numerical aperture as a terminal element of the optical system, before the sample to be analyzed.
Generally, microscopy optics is characterized in that it can increase the image resolution in order to discern microscopic details. The technical feature that determines the resolution of a microscope, in the absence of any aberrations, is the numerical aperture of the objective lens.
As far as the lens is concerned, as is known, its numerical aperture (NA) is given by the following formulae: NA=n sin(α) and α=arctan(D/2f), where f is the focal length of the lens and D is the aperture of the objective lens. Therefore, in order to obtain a high resolution, the ratio between diameter and focal length needs to be high. For minimal apertures like those of the cameras typically integrated into smartphones and tablets, the diameter is very small, and hence the focal length of the lens needs to be very short.
Resolution also depends on the aberrations introduced by the optics. The smaller the dimensions, the more any construction defects are influential and the more the aberrations introduced by the lenses become significant. For this reason, the choice of the lens type and construction is particularly important.
The purpose of the above-mentioned adapter is to make the microscopic world (i.e. with a resolution in the order of a micron) available to anyone into a generally compact design. Such an adapter can be used for various applications, from hobbies to analyses in different professional fields, where “in-field” use (i.e. outside a laboratory) of a microscope may be necessary as a working tool. In addition, such adapters can also find application for medical investigations in developing countries, since they generally imply low production costs.
Adapters generally comprise macroscopic lenses and other macroscopic elements integrated with the optics of the image acquisition device, which typically is a cell phone. However, adapters of this kind are not readily usable and, most importantly, are significantly bulky. By way of example, the following will list a number of disclosures concerning known adapters, which however suffer from several drawbacks.
Patent publication US 2014/0362239 A1 discloses a lens structure that includes an elastomer formed as a lens. The lens has a planar surface and a curved surface opposed to the planar surface. The elastomer of the lens structure may be formed of a base polymer polydimethylsiloxane (PDMS) material. When the lens structure is applied onto the window that protects the optics of an electronic device, such as a cellular phone or a tablet, such device, in the preferred embodiment, can function as a portable microscope. By altering parameters of the lens, such as the radius of curvature, it is possible to achieve a wide range of magnification.
Patent publication WO 2012/058641 A2 discloses a system and methods for enhancing the imaging of cameras included with wireless mobile devices, such as cellular phones or tablets. The system includes a releasable optical attachment for imaging skin surfaces and cavities of the body. The releasable optical attachment comprises elements for optical enhancement elements, such as magnifying lenses, illumination diverting elements, and filters. Images can be viewed and analyzed on the mobile device, or transmitted to another device or another location for analysis by a person or software. The results can be used to provide diagnosis, or for a variety of other applications, including image comparison over time and product recommendations.
Publication PLoSONE Vol. 6 issue 3 e17150 “Cell-Phone-Based Platform for Biomedical Device Development and Education Applications” (Zachary J. Smith, et al., March 2011) concerns the development of two adapters for a commercial cell phone, which transform the lens integrated into the phone and the image sensor into a microscope with 350× magnification and a visible-light spectrometer. The microscope can operate in polarized microscopy transmission mode and has shown to have a resolution of 1.5 microns and a usable visual field of approx. 150×150 microns without image processing, and approx. 350×350 microns with subsequent image processing.